If you're not on the Benghazi panel, Chairman Trey Gowdy said Sunday, shut up — and that includes fellow Republicans.

In an appearance on CBS's "Face the Nation," the South Carolina Republican and former federal prosecutor brushed aside assertions that the panel charged with investigating the 2012 terror attack has lost credibility in the wake of a string of embarrassing comments — from a gaffe on the part of House Majority Leader Kevin McCarthy to speculation by New York Republican Richard Hanna to the explosive allegations from a former GOP Benghazi staffer. "There are three people who don't have any idea what they're talking about," Gowdy said. "Two of my colleagues, the two Republican members of the conference, have never asked for an update on our committee, they couldn't name three witnesses we've talked to, they couldn't tell you a single document production that we have received and the former staffer left in June, so he has no idea what we've done since June.

"I have told my own Republican colleagues and friends, 'Shut up talking about things that you don't know anything about,'" he told host John Dickerson.

Clinton is scheduled to appear Thursday before Gowdy and the rest of the bipartisan panel.

In an appearance on the same show, the panel's ranking Democrat, Maryland's Elijah Cummings, said Gowdy was a "good man" who had been pressured by "the right" to turn the Benghazi Committee into an attack on Clinton.

"He's now trying to shift back to where we should have been all along, looking at the Benghazi incident," Cummings said.

The 12-member Benghazi Committee — seven Republicans and five Democrats — was created in May 2014 and charged by Speaker John A. Boehner with consolidating House probes into the 2012 terror attack in Libya that left four Americans dead.